Pulse radar arrangement

ABSTRACT

A pulse radar system has a high-frequency source, which supplies a continuous high-frequency signal and is connected on the one side to a transmission-side pulse modulator and on the other side to at least one mixer in at least one receive path. A pulse modulator is connected upstream of the mixer with regard to its connection to a receiving antenna. The mixer evaluates a radar pulse reflected by an object together with the signal of the high-frequency source. This system does not require a ZO switch and is insensitive to interference.

FIELD OF THE INVENTION

[0001] The present invention relates to a pulse radar system, inparticular for close-range pulse radar applications in motor vehicles.

BACKGROUND INFORMATION

[0002] Radar sensors are used in automotive engineering for measuringthe distance to objects and/or the relative speed with respect to suchobjects outside of the motor vehicle. Examples of objects includepreceding or parked motor vehicles, pedestrians, bicyclists, or deviceswithin the vehicle's surroundings. The pulse radar functions, forexample, at 24.125 GHz and may be used for the following functions, stop& go, precrash, blind spot detection, parking assistant, and backup aid.

[0003]FIG. 1 shows a schematic representation of a conventional radarsystem having a correlation receiver. A pulse generation 302 causes atransmitter 300 to transmit a transmission signal 306 via an antenna304. Transmission signal 306 hits a target object 308, where it isreflected. The receiving signal 310 is received by antenna 312. Thisantenna 312 may be identical to antenna 304. After received signal 310is received by antenna 312, the signal is transmitted to receiver 314and subsequently supplied via a unit 316 having low pass andanalog/digital conversion to a signal evaluation 318. The specialfeature of a correlation receiver is that receiver 314 receives areference signal 320 from pulse generation 302. Receiving signals 310which are received by receiver 314 are mixed in receiver 314 withreference signal 320. As a result of the correlation, conclusions may bedrawn, for instance, as to the distance of a target object, on the basisof the temporal delay between the transmitting and receiving of theradar impulses.

[0004] A similar radar device is described in German Patent ApplicationNo. DE 199 26 787. In this context, a transmission switch is switched onand off by the impulses of a generator so that a high-frequency wavegenerated by an oscillator and conducted via a termination hybrid to thetransmission switch is switched through to the transmission antennaduring the pulse duration. A reception unit also receives the outputsignal of the generator. The received signal, i.e., a radar pulsereflected by an object, is combined with the oscillator signal, whichreaches the mixer via a reception switch, and evaluated during apredefined time window.

[0005] U.S. Pat. No. 6,067,040 also uses a transmission switch that isswitched on and off by generator impulses. Separate paths for I and Qsignals are provided for reception of the reflected radar pulses. Alsoin this instance, the received signal is only mixed and evaluated duringa predefined time window. Both in the radar device according to DE 19926 787 and in U.S. Pat. No. 6,067,040, the generator signal firstreaches a reception switch/pulse modulator.

SUMMARY

[0006] The measures of the example embodiments of the present inventionmake possible a continuous control of the mixer(s) on the receptionside, which has the advantage that changes in the radar pulses and theirgating does not have a disadvantageous effect on the mixers and theiroperating points.

[0007] Since the mixer(s) are continuously activated by a high frequencysource, compared to the solutions according to DE 199 26 787 or U.S.Pat. No. 6,067,040, an LO (local oscillator)—modulator or an LO highfrequency switch are omitted, and there are no LO pulses. Consequently,changes of pulse modulators, and their activation have no effect on themixers and their operating points.

[0008] The pulse radar device according to the present invention is ableto be broadened to cover several receiving paths, whereas the highfrequency source for controlling the mixers on the receiving side has tobe provided only once.

[0009] Because the design has several receive paths, various distancecells may be evaluated simultaneously. A flexible change of theoperating manner may be undertaken:

[0010] a plurality of receiving channels may be operated in parallel,

[0011] I/Q demodulator operation and individual operation are possible,

[0012] a plurality of antennas may be operated in parallel(multi-receiver principle),

[0013] the pulse duty factors may be selected to be different in thetransmit and receive path,

[0014] the pulse duty factor in the receiving range may be one (purepulse Doppler radar),

[0015] The radar pulses may vary with respect to their repetitionfrequency and/or pulse duration to increase the interference protection,

[0016] the power of the reception pulses may be split among a pluralityof receive paths in the case of target objects that are too strong inclose range, so that overloading of subsequent received-signalamplifiers is prevented,

[0017] a PN code may be provided with a reception sequence correspondingto the set distance,

[0018] a cross echo analysis is possible, and

[0019] the superimposition of two orthogonal codes in the transmit pathmay be provided as well as evaluation of, in each case, only one of thetransmitted orthogonal codes per receive path on the reception side.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The exemplary embodiments of the present invention are explainedin greater detail on the basis of the figures.

[0021]FIG. 2 shows a block diagram of a pulse radar system according toan example embodiment of the present invention.

[0022]FIG. 3 shows a block diagram of a pulse radar system having commonpulse processing.

[0023]FIG. 4 shows a block diagram of a pulse radar system according tothe present invention having a plurality of receive paths.

DESCRIPTION OF EXAMPLE EMBODIMENTS

[0024] The radar sensor according to an example embodiment of thepresent invention shown in FIG. 2 has a high-frequency source 1, whichprovides a continuous high-frequency signal (CW signal). Via a signalsplitter in the form of a termination hybrid 2, this high-frequencysignal reaches on the one side the input of a transmission-side pulsemodulator 3 for transmitting radar impulses to transmission antenna 61and on the other side via a further signal splitter 8 directly to theinputs of two mixers 4 and 5. The additional inputs of these mixers arethen connected via a power splitter 9, e.g., a 3 dB signal splitter, toreceiving antenna 6. In this exemplary embodiment, two mixers 4 and 5are provided, in order to achieve an I/Q (inphase/quadrature phase)capability of the radar system. Signal splitter 9 is used for splittingthe antenna signals on the reception side into the quadrature componentsignals I and Q. If one wishes to do without the I/Q capability, a mixeris sufficient. Then, of course, sub-assemblies 8 and 9 are also notneeded. Mixers 4 and 5 are designed, for example, as balanced mixers inthe form of a RAT-RACE hybrid (compare this in particular to European EP685930 A1, which describes the configuration of such a RAT-RACE hybrid).

[0025] Transmission-side pulse modulator/switch 3 is controlled via apulse signal source 10 and a transmission gate circuit 101. A commonpulse modulator 7 is assigned to the two mixers 4 and 5, and it ispositioned in the receive path between antenna 6 and the additionalsignal splitter 9. The control of this pulse modulator 7 is performedstarting from pulse signal source 111 via a delay circuit 211 and areceiving circuit arrangement 212.

[0026] If a radar pulse reflected by an object travels from antenna 6across power splitter 9 to mixers 4 or 5, the envelope curve of thereceived pulse (IF signal) is formed from the continuous signal of thehigh-frequency source and the reflected radar pulse during the time inwhich the pulse modulator allows the signal of high-frequency source 1to pass. This mixed signal/envelope curve is amplified by broadband ZFamplifiers 411 or 412 with a bandwidth of, e.g., 1 MHz to 1 GHz, andsupplied to a reception scanner 413 or 414. This occurs separately forthe I and the Q channel (separate receive and evaluation paths for thereceived I and Q signal). In this context, mixer 4 and possibly alsomixer 5 has to have a ZF bandwidth of likewise 1 GHz, in order not towiden the reflected radar pulse and thereby lose the object resolution.

[0027] Time-delay circuit 211 is necessary to be able to compare theduration of the received radar pulse and to obtain distance informationtherefrom. After a defined time period following the generation of thetransmission pulse that corresponds with the pulse duration for thedesired distance cell, a particularly short scanning pulse is applied toa broadband scanner 413 and 414, respectively, and the scanner scans theoutput signal of ZF amplifier 411 and 412, respectively, in the selecteddistance cell. In this context, the duration of the scanning pulse is inthe order of magnitude of the transmission pulse width and the ZF pulsewidth. This occurs at the rate of transmission pulse generation, onlyaccordingly delayed. The variation in delay time allows the scanning ofthe desired distance range in the same manner as SRR (short rangeradar). The scanner detects voltages different from 0 and thus detectsthe pulse return after the desired duration. Noncoherent pulseintegration is possible which improves the signal to noise ratioproportionally to SQRT (n), n being the number of integrated pulses.

[0028] The preparation of the scanning pulses for scanners 413 and 414,as well as the control pulses for pulse modulators 3 and 7 may,according to FIG. 3, also jointly take place by a shared pulse signalsource 100.

[0029] The following additional advantages are yielded by thearchitecture of the pulse radar device according to the presentinvention:

[0030] Because the signal of high frequency source 1 is constantlypresent as a CW signal at mixer 4 and 5, respectively, and is not pulsedas in the case of the SRR, a substantial improvement comes about in thenoise figure, and therewith the possibility of effectively widening thedetection range. Besides that, no disadvantageous displacements canoccur in the operating points of the mixers by preconnected pulsemodulators/pulse switches.

[0031]FIG. 4 shows an exemplary embodiment having a plurality of receivepaths, two in this particular instance. The individual receive paths maybe configured as shown in FIG. 2 or 3. However, in order to point outadditional design variants of the present invention, the receive pathsshown in FIG. 4, in deviation from FIGS. 2 and 3, have the followingdifferences:

[0032] Instead of a common pulse modulator 7 on the receive side, eachmixer 4, 5 and 41, 51, respectively, has a separate pulse modulator 71,72 and 711, 721, respectively, which may be controlled independently ofthe respective other mixers of the same receive path via a correspondingpulse signal source 11, 12 and 111, 121, respectively, a time-delaycircuit 21, 22 and 211, 221, respectively, and a reception gate 212, 213and 214, 215, respectively. The individual receive paths may have attheir disposal either a common receiving antenna 61 or each haveseparate receiving antennas 61, 62, 63. Additional downstream signalsplitters 81, 82 are required to connect mixers 41, 51 of the furtherreceive paths to high-frequency source 1, which is shared by all receivepaths.

[0033] As a result of the at least two receive paths and separatecontrol of reception-side pulse modulators 71, 72 and 711, 712,respectively, each having adjustable time-delay circuits 21, 22, 211,221 at different delay times, different modes of operation are possibleas well as a faster change between these different modes of operation asa function of the needs of the vehicle operator. As a result, inparticular

[0034] a plurality of channels (mixers) may be operated in parallel,

[0035] a plurality of antennas may be operated in parallel(multi-receiver principle),

[0036] the pulse duty ratio may be selected to be different in thetransmission and receive path(s);

[0037] the pulse duty factor may be one (pure pulse Doppler radar),

[0038] the transmission pulses may be varied in their repetitionfrequency and/or pulse duration particularly for increasing theinterference protection,

[0039] I/Q demodulator operation and individual channel operation arepossible,

[0040] in response to using double or triple transmission pulse power,at the same sensitivity, a plurality of reception cells may be evaluatedat the same time using appropriate algorithms for discovering objects,

[0041] the distance cells may be adjusted by scanning or masking out thereceived signal,

[0042] the reception pulse power may be split in the case of targetobjects that are too strong in close range so that in particularoverloading of subsequent amplifiers is prevented, and

[0043] a cross echo analysis is possible.

[0044] If coded sequences of pulses (PN coding) are transmitted, themodulators in the receive paths, in this case, for example, phaserotators, are controlled by a reception sequence corresponding to theset distance. This contributes significantly to the suppression of falsetargets. The channels monitor different distance ranges.

[0045] In the event that a reception-side device is set to the PN codeof a neighboring device, a cross echo analysis is possible.

[0046] Superimposition of two orthogonal codes may be provided in thetransmit path, and in each case only one of the transmitted orthogonalsignals is evaluated per receive path.

[0047] The transmission-side and reception-side pulse signal sources 10,100, 11, 12, 111, 121 or only the reception-side pulse signal sources11, 12, 111, 121 among one another are phase-coupled with one another,particularly in the case of a plurality of receive paths, in order toachieve specified time relationships particularly for the simultaneousmonitoring of a plurality of reception cells.

1-14. (Canceled).
 15. A pulse radar system for a close-range pulse radarapplication for a motor vehicle, comprising: a high-frequency sourceconfigured to emit a continuous high-frequency signal; a signalsplitter, the high-frequency source being connected to the signalsplitter; a transmission-side pulse modulator configured to emit radarpulses, a first side of the signal splitter being in contact with thetransmission-side pulse modulator; at least one mixer in at least onereceive path, a second side of the signal splitter being in contact withthe least one mixer, the at least one mixer being controlled by thecontinuous high-frequency signal of the high frequency source for anevaluation of at least one reception signal, which is made up of atleast one radar pulse reflected by an object; and a reception-side pulsemodulator connected upstream of the at least one mixer with respect to aconnection to a receiving antenna.
 16. The pulse radar system as recitedin claim 15, wherein the at least one mixer includes at least two mixersin the receive path, the at least two mixers being connected via anadditional signal splitter to the high-frequency source.
 17. The pulseradar device as recited in claim 16, further comprising: a furthersignal splitter to transmit quadrature component signals connectedupstream of the at least two mixers, with respect to their connection tothe receiving antenna.
 18. The pulse radar device as recited in claim16, further comprising: a separate reception-side pulse modulatorconnected upstream of each of the at least two mixers in the receivepath, with respect to their connection to the receiving antenna.
 19. Thepulse radar device as recited in claim 18, wherein each respective oneof the reception-side pulse modulators being controllable via a separatepulse signal source, time-delay elements having different delay timesbeing provided between the pulse signal sources and the respectivereception-side pulse modulators.
 20. The pulse radar device as recitedin claim 15, further comprising: a pulse signal source, thetransmission-side pulse modulator being controllable by the pulse signalsource, at least one of a repetition frequency and a pulse duration ofthe pulse signal source being variable for increasing interferenceprotection.
 21. The pulse radar system as recited in claim 15, whereinat least one further receive path is provided having correspondingreceiving antennas, corresponding reception-side mixers, andcorresponding reception-side pulse modulators.
 22. The pulse radarsystem as recited in claim 21, wherein the at least one further receivepath further includes corresponding signal splitters and correspondingpulse signal sources.
 23. The pulse radar system as recited in claim 21,wherein connection of the corresponding reception-side mixers of thefurther receive paths takes place via additional signal splitters whichare downstream from the high-frequency signal source.
 24. The pulseradar system as recited in claim 21, wherein a plurality of distancecells are able to be evaluated at the same time by correspondingevaluation devices.
 25. The pulse radar device as recited in claim 15,where the transmission-side pulse signal source and the reception-sidepulse signal source are phase-coupled with one another.
 26. The pulseradar device as recited in claim 21, wherein the correspondingreception-side pulse signal sources are phase-coupled with one another.27. The pulse radar system as recited in claim 15, wherein a pulse dutyfactor of the radar pulses in a transmit path and in the receive pathare different.
 28. The pulse radar system as recited in claim 21,wherein radar pulses are P.N. coded, the corresponding reception-sidepulse modulators being controllable using a reception sequencecorresponding to a set distance.
 29. The pulse radar system as recitedin claim 28, wherein a cross echo analysis is provided, a reception-sidedevice being set to a P.N. code of a neighboring device.
 30. The pulseradar system as recited claim 15, wherein a superimposition of twoorthogonal codes is provided in a transmit path, and the receive pathevaluates in each case only one of the transmitted orthogonal signals.